CHAPTER VI.
THE EXAMINATION OF THE HEAD.
I. METHODS OF EXAMINATION.
1. Removal of Skull-Cap. For the section of the head the cadaver is placed upon its back with its head near the end of the table. The head may be elevated by a block placed beneath the neck, or it may be elevated and at the same time firmly held in position by the use of a special head-rest, different varieties of which are offered by instrument-makers. It is better to use the simple block of wood and to control the position of the head with the hands during the operation. The prosector takes his position behind the head of the table. The hair of the cadaver is then arranged in such a manner as to be out of the way, and protected by towels so that it will not become matted with blood and bone-dust. When the hair is short it is parted in a line extending from just behind the ears across the vertex. The shape of the head and the degree of baldness will determine the exact position of the primary incision through the scalp; sometimes it must be made farther back than the line connecting the ears in order that the incision may be concealed. In the great majority of cases it will be made as follows: The head is steadied with the operator’s left hand, and turned as far to the right as possible. The point of the cartilage-knife is then inserted into the scalp, just within the hair-line, behind the left ear, and with the belly of the knife the scalp is cut through to the periosteum, in the line of the hair-part, over the vertex, and as the head is turned to the left, down to the hair-line behind the right ear, the knife, as it approaches the end of the incision being raised so as to make the point finish the cut. This scalp-incision should be made with a strong and quick drawing movement, but the knife should not be pressed so firmly against the bone as to cut through the periosteum, else hemorrhages, collections of pus. etc., may escape before they are seen.
The scalp is next loosened anteriorly by means of the hands, using the tip of the cartilage-knife occasionally to nick the fascia and thus facilitate the working forward of the anterior flap until it has been loosened as far as the supraorbital ridges anteriorly and down to the level of the beginning and ending of the incision made across the vertex. When sufficiently loosened the anterior scalp-flap is turned over the face, and stretched over the chin, where it will remain, out of the way, and with both face and hair protected. The posterior flap of the scalp is then worked back to the same level at the sides and to the lower border of the occipital protuberance posteriorly. It is then turned under between the back of the neck and the wooden block. In stripping the scalp the greatest care should be taken not to cut or tear off the periosteum. Scars, tumors, adhesions, traumatic lesions, etc., in the scalp should be carefully worked out and described as the flaps are loosened. The convex margin of the fascia of the temporal muscles is now cut with the point of the cartilage-knife and the muscles are stripped down on both sides to the level of the folded-over scalp-flaps, where they are either left hanging down out of the way or are cut off and laid aside. If they cannot be easily stripped down, they may be scraped off with the chisel. Some prosectors remove them at the same time with the scalp, but this is usually not well done. The skull now should be bare, except for the periosteum, down to the level of a line passing just above the upper margin of the orbits anteriorly, at the sides just above the aural opening, and posteriorly just below the occipital protuberance.
The periosteum is next removed over the entire cranial surface by means of the chisel, bone-scraper or dull knife. In medicolegal cases particularly it is of the greatest importance that the periosteum be removed in this way and the surface of the skull-cap carefully examined. In ordinary cases the periosteum is often left attached to the skull-cap when the external examination shows no pathologic conditions to be present.
After the examination of the periosteum and external surface of the cranium the skull-cap is removed by sawing in such a way that a space large enough for the convenient and safe removal of the brain is afforded. This may be done in several ways. A circular incision may be made through the skull around its entire circumference just above the level of the folded-over flaps of scalp. The left hand should be protected by a folded towel. The head is held firmly in the left hand and turned slightly toward the left. The saw-cut is then begun anteriorly about ½ cm. above the supraorbital margins, and continued around to the right, while the head is turned more and more to the left. The ear should be held down out of the way by an assistant. The saw-cut is continued then at the same level to the posterior median line just below the level of the occipital protuberance. The saw is then removed and the head turned as far as possible to the right; the saw-cut is then continued around the left side from the posterior median line until the beginning of the cut in front is reached and the circular incision is complete.
Fig. 26.—Author’s method of removing skull-cap.
Another method of sawing the skull-cap is to saw in two planes, forming an angle just behind and below the ear (angular method). The anterior cut is made above the hair-line of the forehead and carried down at the sides to meet just below and behind the ear the posterior semicircular cut made at this level. A modification of this method is to make the anterior and posterior cuts join at a sharper angle in front of the ears. Both of these methods have for their object the prevention of disfigurement of the forehead. When the circular method is used a depression or ridge is often seen in the forehead, after the restoration of the body, due to the slipping of the skull-cap after it has been replaced. Such an accident may happen even when the bones are wired together, unless great care has been taken in wiring.
A more satisfactory way of opening the skull, and one that makes slipping of the skull-cap after restoration practically impossible, is the method used by the writer, and illustrated in Fig. 26. The scalp-incision and the folding back of the flaps are carried out as described above. The right half of the anterior flap of the scalp is then taken in the left hand and used to control the position of the head, the latter being turned to the left as far as possible. An oblique saw-cut is then made on the right side in a line extending from the posterior margin of the site of the posterior fontanel, over the right parietal eminence toward the right mastoid prominence. The sawing begins on the greatest convexity and is continued upward a slight distance beyond the median line, and downward far enough to cross the level of the connecting horizontal cut to be made later at a level just above the aural canal. The left half of the posterior scalp-flap is now taken into the left hand and used to steady the head while it is turned over to the right as far as possible. A similar oblique cut is then made on the left side, crossing the one made on the right, in the median line, behind the site of the posterior fontanel, and extending down across the left parietal eminence in the direction of the left mastoid prominence. While the head is still held by the left half of the posterior scalp-flap a horizontal saw-cut is begun on the left side, just above the aural canal, intersecting the oblique cut posteriorly and continued around to the front at a level just above the supraorbital ridges. When the frontal region is reached the head is steadied by holding the left half of the anterior portion of the scalp-flap. When the horizontal cut reaches the right temple the right half of the anterior flap is taken in the hand, and the head turned to the left while the cut is carried around the right temporal region to intersect the right oblique cut. When the skull-cap is removed there is formed an interlocking joint (Fig. 27) which under ordinary conditions holds the restored skull-cap firmly without wiring and without the formation of a ridge or crease on the brow, since the bone cannot slip. It is best, however, in the event of the shipment of a cadaver by rail to wire the bones to prevent any forcible dislodgement.
Fig. 27.—Skull-cap after removal, showing posterior interlocking joint.
Whatever method is used the greatest care should be taken to saw the skull-cap without injuring the brain. The difference in thickness of different portions of the cranium must be borne in mind. Sight, sound and “the feel” are taken as guides. The outer and inner tables, the diploë, and the dura have an entirely different resistance and give a different sound. The saw-dust of the outer table is white, that of the diploë red, that of the inner table white. As soon as the saw strikes the dura a peculiar “rustling” or “scraping” sound is heard, and this should be taken as the warning to stop sawing. On curved surfaces it is best to begin sawing on the greatest convexity and to continue until the saw is through and then to extend the cut from this point. The sawing should be done lightly and quickly, without too strong pressure. Set the saw carefully at first, to avoid slipping. The small bone-saw is usually used for this operation; saws attached to electric or dental engines are sometimes employed. Care should be taken to bring the beginning and ending of the saw-cut into the same plane; and the oblique cuts should be symmetrical.
As soon as the sawing is completed, no matter what method is used, the T-chisel or skull-opener (Fig. 12) is used to spring off the skull-cap. The chisel-blade is inserted into the saw-cut in the right frontal region, and turned sideways with a quick, powerful movement of the right hand. Any portions of the inner table not completely sawed through (usually in the region of the petrous portion of the temporal) are thus broken, and the dura is loosened sufficiently from the inner table to allow the prosector to introduce the fingers of the right hand beneath the skull-cap in the frontal region and to hold down the dura while the fingers of the left hand inserted into the frontal saw-cut pull the skull-cap backward with a powerful tug, completely separating it from the dura, unless the dura is adherent throughout, as is the case in very young children, old people, and in certain pathologic conditions. In the latter case it may be necessary to cut the dura along the line of the horizontal saw-cut and to remove it with the skull-cap, cutting the falx as the skull-cap is lifted. In young children the dura must always be removed with the skull-cap. In the case of pathologic adhesions an attempt should be made first to separate them from the lamina vitrea by cutting them with a knife or chisel-blade inserted through the saw-cut. As the adhesions are severed the skull-cap is lifted gradually backward. Too much force should not be used in jerking off the skull-cap, else the brain may be damaged. Whenever possible the dura should be left intact, as a better judgment is thereby obtained of the intradural pressure, and there is less danger of losing the contents of the subdural space.
Some prosectors use hammer and chisel to remove the skull-cap. This is a bad method, particularly so in the case of medicolegal autopsies, as artificial fractures of the skull may thus be produced. It is safest never to use a hammer in the opening of the skull.
The skull-cap is examined as soon as taken off. If the periosteum was not previously removed it is now scraped off, and the skull-cap examined against the light. After its complete examination the operator proceeds to the removal of the brain.
2. Removal of the Brain. The convexity of the dura is first examined. The narrow-bladed brain-knife or long section knife (Fig. 3) is now taken in hand, and with the cutting edge directed upward the point of the blade is inserted into the anterior end of the superior longitudinal sinus and the sinus cut open as far posteriorly as the opening in the cranial vault will admit. Its walls and contents are then examined. With cutting edge outward the point of the brain-knife is then inserted through the dura just to the left of the anterior end of the falx and the dura cut around to the left at the level of the horizontal saw-cut. The knife is then inserted through the dura just to the right of the falx and the dura cut in the same way on the right side. The two halves of the dura are now loosened from the convexity of the brain by breaking the blood-vessels connecting the dura with the inner meninges. The index-finger is swept over the convexities and along the sides of the longitudinal sinus, tearing the pial veins. Pathologic adhesions should be carefully worked out. The finger is then used to raise the falx anteriorly so that the point of the brain-knife can be introduced beneath it to cut it upward and forward. The dura is then carefully examined and turned back over the brain and allowed to hang down over the occiput. The inner meninges over the exposed portion of the brain are now examined; and the brain is then removed as follows: The four fingers of the left hand are placed beneath the frontal lobes, lifting these sufficiently for the prosector to be able to cut the I, II, III, IV and VI cranial nerves, the carotids and pedicle of the hypophysis down to the tentorium cerebelli. The tentorium is then cut with the tip of the brain-knife, which is held perpendicularly, by a gentle up-and-down sawing motion, from left to right along the superior border of the petrous bones. The V, VII, VIII, IX, X, XI and XII cranial nerves are then cut as closely as possible to their exits. As they are cut the brain is lifted gradually more and more, and supported by the left hand. When all the connections have been cut except the cord and vertebral arteries these are severed by the myelotome (Fig. 4), or by the brain-knife, the point of which is put down through the foramen magnum as far as possible, and the cord and vertebral arteries severed by a transverse cut made from left to right as nearly horizontal as possible. The knife is now laid aside and the first two fingers of the right hand put beneath the two cerebellar lobes so that the medulla and portions of cervical cord fall between these fingers, which are then used to lift them upward and backward. The freed brain is now rolled over backward out of the cranial cavity upside down onto the palm of the left hand, and is then placed upon a board, tray or dish ready for examination. If the cord has already been removed, any portion remaining is taken out with the brain. In case the cord has been freed and is to be removed with the brain it is only necessary to cut the vertebral arteries and then to lift up the brain, drawing the cord up through the foramen magnum.
3. Section of the Brain. (Modified Virchow Method.) The brain as it is taken from the cranium is placed upside down, with occipital lobes toward the prosector. The basal meninges and blood-vessels are then carefully examined. The hemispheres and convolutions are separated and the arachnoid torn by the tip of the index-finger or the handle of a scalpel; and the branches of the cerebral vessels to their deepest ramifications are thus exposed, giving a complete picture of the circle of Willis and all of its branches to the point where they enter the brain-substance. The larger vessels are opened by transverse or longitudinal cuts and their walls and contents noted. The brain is then turned over, and the meninges examined over the entire convexity. The pia and arachnoid are then removed together over the entire convex and median surfaces of the hemispheres. If the blood-vessels between the convolutions are seized with the forceps the meninges can be easily stripped off, the fingers aiding the forceps, using great care not to tear the brain substance. The meninges are removed about half-way down the outer sides of the hemispheres and are there left intact so as to hold the pieces of brain together after it has been cut, and so permit orientation. The cortical surface is then examined; if bloody, it should be washed with a weak stream of water.
Fig. 28.—Method of examination of brain. Opening of left ventricle. Line showing direction of cuts. (After Nauwerck.)
The hemispheres are now separated until the corpus callosum comes into view. The left hemisphere is then held by the left hand, with the thumb on the median surface and the fingers on the outer and under sides, so that the hemisphere is turned outward and yet raised slightly at the same time, thus stretching the corpus callosum over the cavity of the left lateral ventricle. The point of the narrow brain-knife (Fig. 3) with cutting edge upward is then introduced with great care through the corpus callosum about midway between the genu and splenium and close to the gyrus cinguli (gyr. forn., Fig. 28). The corpus callosum at this point is about 2 to 3 mm. thick and it is gently nicked with the point of the knife until an opening is made into the cavity of the ventricle. The knife-point must not be allowed to slip through to damage the basal ganglia beneath. Into the small opening thus made the brain-knife, held nearly horizontal, with cutting edge upward, is introduced and the corpus callosum cut forward until the anterior horn of the ventricle is reached. The point of the knife is then passed into the horn and the knife-handle raised and turned over forward, cutting slightly outward through the frontal lobe to its apex and disclosing the anterior horn. The knife is then reversed, held horizontally, with cutting edge upward, and the corpus callosum cut posteriorly from the beginning of the first cut, until the posterior horn is reached, when the point of the knife is inserted into the horn and the knife turned over toward the operator, cutting backward and somewhat outward through the occipital lobe to its apex and opening up the posterior horn. (See Fig. 28.) By this method the lateral ventricle is opened first at the highest point of its cavity, and the fluid contents collect in the anterior and posterior horns so that the amount and character can be easily noted.
Fig. 29.—Section of brain. Ventricles opened. Lines show direction of large longitudinal incisions through brain-substance. (After Nauwerck.)
The left hemisphere is now turned still more to the left, and with the brain-knife a broad, smooth cut is made through it downward and outward at an angle of 45°, reaching nearly to the cortical surface, in a line connecting the cut through the frontal lobe with that through the occipital and passing along the outer borders of the corpus striatum. The left hemisphere is thus separated in the form of a prism-shaped mass having a convex under surface. (See Fig. 29.) The severed hemisphere falls back by the force of its own weight and the flat cut-surface of the cerebrum is then bisected by a cut made at right angles to it, from before backward, and extending nearly to the cortical surface. (See Fig. 29.) In the case of both of these large incisions of the hemisphere the severed parts are left connected by a small portion of cortical tissue and the pia. The knife should be perfectly dry and clean while making these cuts, and the cut surfaces should not be touched with the fingers or knife-blade, or wet with water, until they have been carefully inspected. Other straight parallel cuts may be made through the brain substance toward the cortex, the severed portions being left connected by the pia so as to permit future orientation.
The right lateral ventricle is now opened. The four fingers of the left hand are placed outside and beneath the right hemisphere with the thumb on the median surface, gently raising the hemisphere toward the left, taking care to see that the corpus callosum is not pulled over to the right of the median line. The knife is held in the right hand beneath the left one. The right ventricle is then opened in the same way as the left, beginning in the middle of the corpus callosum near to the gyrus cinguli, and opening first the anterior horn and then the posterior. The operation is somewhat more difficult on the right side than it is on the left, owing to the lack of tension in the cut corpus callosum, so that greater care must be taken to avoid injuring the floor of the ventricle. After the opening of the ventricle the right hemisphere is cut by long parallel incisions made in the same way as on the left side. (See Fig. 29.)
Some prosectors in opening the right ventricle prefer to turn the board around so that the frontal lobe points to the operator. The right hemisphere is then held in the left hand and the right ventricle opened just as if it were the left ventricle, except that the posterior horn is opened before the anterior. The method given above can be just as easily learned, and time is saved by not turning the board around twice, as is necessary in the latter case.
After the right ventricle has been opened the corpus callosum and fornix are raised by the thumb and index-finger of the left hand, putting the septum pellucidum on the stretch. The narrow brain-knife is then introduced through the interventricular foramen from the right, its blade flat, with cutting edge directed forward and upward, and the fornix and the corpus callosum are cut anteriorly, exposing the cavity of the septum pellucidum. To expose the third ventricle, the corpus callosum, septum pellucidum and fornix are then lifted up and laid back from the velum chorioides. The tela chorioidea is then, with the chorioid plexus of the third ventricle, pulled backward from over the pineal body and the corpora quadrigemina, care being taken not to tear away the pineal body. The veins entering the tela from the great ganglia are cut with the point of the knife. The right descending posterior pillar or crus of the fornix is then lifted with the thumb and index-finger of the left hand, the brain-knife on the flat side with cutting edge to the right is introduced beneath it, and the crus is cut toward the right. The corpus callosum, fornix and tela are then turned over to the left (see Fig. 29), fully exposing the pineal body and the corpora quadrigemina.
The cerebellum and medulla are now supported by the index-finger of the left hand placed beneath the latter; while the brain-knife is held nearly horizontally in the right, and a deep sagittal cut is made into the vermis exactly in the median line so as to make a small opening into the fourth ventricle. The point of the knife with cutting edge upward is then introduced into this opening and the incision through the vermis increased anteriorly and posteriorly until the two cerebellar hemispheres fall apart and the fourth ventricle is wholly opened. The point of the knife, with cutting edge upward may then be introduced into the posterior opening of the aqueduct and the latter opened to the third ventricle, the pineal body being removed before the cut through the roof of the aqueduct is made. In the Virchow method the corpora quadrigemina and the vermiform portion of the cerebellum are sectioned in the median line by a cut opening up both aqueduct and the fourth ventricle. Other prosectors open the aqueduct from the third ventricle toward the fourth. The left cerebellar hemisphere is now cut through in the line of the middle branch of the arbor vitæ, exposing the dentate nucleus. Each half of the hemisphere is again bisected by a cut made at right angles to the surfaces exposed by the first cut. The right cerebellar hemisphere is then similarly sectioned.
The section of the brain now shows all of the ventricles and their relations, as well as the condition of a large part of cerebral and cerebellar brain-substance. (See Fig. 29.) All cut portions are connected with each other and it is possible to fix the entire brain as it now stands and later find no difficulty in topographic orientation. There still remains, however, the demonstration of the conditions in the basal ganglia, pons, medulla, etc. These structures are best shown by transverse cuts made across the entire brain as it lies after the opening of the ventricles. The hemispheres may be cut singly, but it is better to cut both of them at the same time, using a dry blade and drawing the knife from left to right, making identical cuts on the two sides, that the histologic features may be compared. The transverse cuts may be made in the same region as recommended in the method of Pitres (see below), or they may be made closer together. As the cuts are made the sections are separated from each other by the knife-blade and the cut surfaces examined. After the cerebrum has been cut transversely in this way the peduncles, pons, medulla and cervical cord are elevated on the index-finger of the left hand and also sectioned transversely and the cut surfaces examined. If the index-finger be placed beneath the medulla parallel with its long axis, and medulla and pons raised up the cerebellar lobes fall to the side out of the way. All transverse cuts are made from left to right and so deep that only a small portion of brain-tissue, or the basal meninges hold the parts together for future orientation. The brain is now completely sectioned, with all parts preserved and capable of being restored to their normal relations. The parts may be re-assembled and the entire brain put into the fixing fluid, when it is desirable to save the entire organ for microscopic study.
Fig. 30.—Method of Pitres. 1, Sectio præ-frontalis; 2, Sectio pediculo-frontalis; 3, Sectio frontalis: 4, Sectio parietalis; 5, Sectio pediculo-parietalis: 6, Sectio occipitalis.
Other Methods of Opening Brain. For the demonstration of large localized pathologic conditions the brain may be opened by a very simple method of transverse or sagittal incisions extending entirely through the organ. The broad-bladed brain-knife should be used and the blade should be wet. The cuts should be made symmetrically on the two sides and with due reference to anatomic landmarks. They may be made either from the convexity or from the basal side.
The method of Pitres (see Fig. 30) is also employed for the same purpose. After the inspection of the meninges and basal vessels and opening of lateral ventricles, the brain is divided into three parts, consisting of the two hemispheres and one part made up of the cerebellum, pons and medulla. The anterior ends of the cerebral peduncles are cut transversely in front of the corpora quadrigemina, and the hemispheres are then separated by a sagittal median incision through the corpus callosum, septum pellucidum, commissure of third ventricle, substantia perforata posterior, tuber cinereum and infundibulum, the optic chiasm and neighboring optic tract having first been removed. The hemispheres are then cut as follows: The hemisphere is laid upon its median surface with the occipital lobe toward the operator. The four fingers of the left hand are then put into the central fissure and six parallel transverse cuts (see Fig. 30) are made through the hemisphere with a dry brain-knife, as follows:
1. Sectio praefrontalis, through the frontal lobe about 5 cm. in front of and parallel to the central fissure, exposing the cortex and medulla of the three frontal convolutions, gyrus orbitalis, and the convolutions of the median surface of the frontal lobe.
2. Sectio pediculo-frontalis, through the “foot” of the frontal convolutions, exposing the three frontal convolutions, anterior end of the island of Reil, gyrus orbitalis, corpus callosum, head of caudate nucleus, anterior portion of lentiform nucleus and lenticular striated portion of the internal capsule.
3. Sectio frontalis, through the anterior central convolution, showing the anterior central convolution, island of Reil, the temporal convolutions, corpus callosum, tail of caudate nucleus, the optic thalamus, middle portion of lentiform nucleus, the anterior portion of the lenticular part of the internal capsule, the external capsule and claustrum.
4. Sectio parietalis, through the posterior central convolution, showing the same, the island of Reil, temporal convolutions, corpus callosum, tail of caudate nucleus, posterior end of optic thalamus and lentiform nucleus, posterior end of the lenticular-optic part of internal capsule, the external capsule and the claustrum.
5. Sectio pediculo-parietalis, through the foot of the parietal convolution, 3 cm. posterior to the fissure of Rolando, showing superior and inferior parietal lobules, temporal convolutions, corpus callosum, extreme posterior portion of optic thalamus and tail of caudate nucleus.
6. Sectio occipitalis, about 1 cm. in front of the parieto-occipital sulcus, showing cortex and medulla of occipital lobe.
After the third cut the fingers of the left hand are taken out of the central fissure. The sections of brain as they are cut are left lying in their order with the posterior face of the cut upward. The same incisions are then made in the other hemisphere and the two series of sections compared. The cerebellum, pons and medulla are then examined as described above.
Section of Brain in Skull. When the skull-cap is removed by a circular saw-cut the brain may be cut through with the saw at the same time; or, after the skull-cap and dura have been removed, the upper portion of the hemispheres may be sliced off by a horizontal cut made at the level of the saw-cut. The portions removed are examined further by sagittal cuts. The lateral ventricles are then examined in the skull, and the remaining portion of the brain either cut transversely in situ or removed and sectioned outside of the cranium. This method is mentioned to be condemned.
For special neuropathologic studies a number of methods have been advised, the main purpose of which has been to preserve intact parts of the brain having definite anatomic relationships so that lesions may be studied by means of serial sections of the entire system involved. The methods of Déjerine and Meynert are employed for this purpose.
Method of Déjerine. After a careful examination of the cortical surface for the presence of lesions, and of the inferior surfaces of the crura for secondary degenerations, the pons is cut horizontally in a plane parallel with the inferior surface of the hemispheres and passing just above the great root of the trifacial. The brain is thus divided into two portions, one consisting of the two peduncles and superior portion of the pons, the other containing the remaining portion of the pons, the cerebellum and the medulla. The cut surfaces of the pons are examined for evidences of degeneration in the pyramidal tracts, and the hemispheres are separated after it has been determined in which one the lesion is located. If the lesion is found to be central the degenerations of importance will be found in the tracts of the internal capsule and in the region of the tegmentum. The hemispheres are then opened by horizontal incisions passing through the superior third of the optic thalamus. If the lesion is cortical the hemispheres are divided into three segments by two transverse vertical incisions, one passing just posterior to the splenium of the corpus callosum, the other just anterior to the knee. The posterior segment consists of the occipital lobe and part of the parietal; the central one contains the regions adjacent to the fissure of Rolando, the middle portion of the temporal convolutions, the basal ganglia, the cerebral peduncle and corresponding portion of the pons; the anterior segment consists of the forepart of the frontal lobe. The segments are then fixed and hardened and cut on a brain-microtome. The anterior and posterior segments are sectioned vertically transversely, the central segment is cut horizontally. By this method cortical lesions may be accurately located, and the entire course of degenerating fibres followed out.
Method of Meynert. This method aims to separate all portions of the brain possessing differences of internal structure that may be taken as indicating difference in significance, and to compare them by weight. The natural furrows or fissures are used as incision-lines, and three series of dissections are made, the first of which, here given, is the separation of the brain into three parts, the brain-mantle, brain-stem and cerebellum. The brain, with pia still intact, is placed base upward, with cerebellum toward operator. The arachnoid covering the fissure of Sylvius is cut or torn, and the island exposed. The three furrows bounding it must be plainly seen. The pia between the optic tract and uncus, as well as that in the middle portion of the transverse fissure between corpora quadrigemina and corpus callosum, is cut, and the under surface of the splenium of the corpus callosum is freed from membranous adhesions to the corpora quadrigemina and the pineal body. When the medulla with pons and cerebellum is now elevated the transverse fissure gapes open, and permits a free look into the lateral ventricles.
The brain-mantle on both sides is now separated from the brain-stem at the basal portion of its frontal end. The knife, held nearly horizontal, is introduced into the fissure between the posterior border of the orbital convolutions and the anterior border of the lamina perforata anterior; and a cut is made slightly downward, not quite parallel with the orbital surface, about 3 cm. anteriorly in the medulla of the orbital convolutions, around the under surface of the head of the corpus striatum. The temporal ends of the brain-mantle are then cut through, the knife moving externally between the temporal lobe and the island, inside between the descending horn of the lateral ventricle and the optic tract. As soon as the inner cut has been extended beyond the outer corpus geniculatum on both sides, the knife is turned downward at right angles, in a curving stroke, to cut through the junction of the occipital lobes with the stem, internally along the portion of the corpus striatum adjacent to the optic thalamus, externally between the junction of the first temporal convolution with the operculum on one side, and the posterior end of the island on the other. When this has been done on both sides the blade of the knife is turned forward in a semicircular stroke. The posterior end of the brain-stem is gradually lifted up out of the mantle by elevating the cerebellum and medulla oblongata. The upper peduncle of the arch of the brain-mantle along the upper border of the island and the outer border of the corpus striatum is severed from the stem as far as the anterior end of the upper border of the island, which bends downward into the anterior border. The peduncle of the fornix with the pedicle of the septum and the lamina of the knee of the corpus callosum are severed close above the anterior commissure, and the knife following the anterior border of the island is carried downward from the head of the corpus striatum. The remaining connections between the frontal lobes and stem are put on a moderate stretch and the incision is completed by bringing the knife back into the first cut made from the opposite direction parallel with the orbital surface over the upper surface of the stem. The three arms of the cerebellum are then severed and the brain-stem, consisting of the island of Reil, the basal ganglia, crura, pons, medulla and cerebellum, is completely freed and lifted out of the mantle.
A combination of the Meynert and Virchow methods is used by many. The lateral ventricles are opened and an incision made along the fornix into the descending horn. The stem-ganglia are then cut out and brain-mantle and stem separated. The hemispheres are then cut by frontal sections made from the anterior end as far as the central convolutions. From the central convolutions backward horizontal sections are then made; the series of sections are numbered in order and fixed and hardened for microscopic examination.
It is evident that the section of the brain can be modified to meet the individual requirements, according to the nature, location and extent of the lesion and the character of the study to be made of the latter. The brain may be fixed and hardened either before or after sectioning.
Fig. 31.—Base of cranium, after removal of brain. (After Nauwerck.)
4. Examination of Base of Cranium. After the section of the brain the prosector returns to the head and examines the basal sinuses (see Fig. 31) by cutting them open with the point of the brain-knife or by using small shears and forceps. When cut open the walls of the sinuses should be laid back for inspection. Ordinarily the sinus transversus, sinus petrosus superior, sinus petrosus inferior, sinus cavernosus and the sinus sigmoideus are opened. The last-named is given especial attention because of the frequency of thrombosis and its involvement from carious conditions of the neighboring portions of the temporal bone. In purulent mastoid inflammation the infection often reaches the meninges by this route. The carotids and the exits of the cranial nerves (see Fig. 31) are then examined. The hypophysis (see Fig. 31) is then removed by making semicircular cuts through the overlying dura mater around the gland and then lifting it out of the sella. This is best accomplished by means of the small scalpel and forceps. It is sometimes necessary to chisel away the overhanging bony parts in order to remove the hypophysis without damaging it. When removed it may be sectioned by a sagittal cut made either to the left or right of the pedicle.
Fig. 32.—Incisions for examination of orbit, ear and nose. x y marks line of incision for exposing nasal tract according to method of Harke.
The basal dura is next removed by means of forceps and knife, chisel or dura-forceps. The bones are then carefully examined for fractures, caries, etc. Particularly in cases of middle-ear disease, meningitis, etc., should the dura be removed from the temporal bone and the latter carefully examined.
5. Examination of the Orbit. When the eye-ball cannot be enucleated anteriorly the orbit may be opened by removing its roof with small bone-chisel and hammer according to the lines of incision given in Fig. 32. The dura is, of course, first removed. The bony plate covering the orbit is thin and easily splintered, so that the chisel should be very carefully used. The pieces of bone should be removed with the forceps. The optic foramen and the superior orbital fissure may be opened at the same time. After the removal of the roof of the orbit the orbital fat and muscles are dissected away until the optic nerve and eye-ball are exposed. The sclera is then seized with the forceps and the eye-ball pulled back and cut quickly around its equator with sharp shears or scalpel. The head should be held so that the eye looks downward, so that when cut the vitreous humor falls out, leaving the retina well spread out over the posterior half of the bulb. If the retina is thrown into folds it may be straightened by blowing into it or filling it with water. After the retina has been examined it may be washed off from the chorioid, leaving it attached around the papilla. The pigment-layer remains attached to the chorioid, and when the latter is examined for the presence of tubercles it should be removed. When removed for microscopic studies the eye should be placed at once in a suitable fixing fluid.
Fig. 33.—Tympanic cavity after removal of tegmen. an, mastoid antrum; ha, hammer-anvil articulation; s, tendon of musc. tens. tymp.; t. musc. tens. tymp.; g, genu of facial nerve; a, auditory nerve; f, facial nerve; n, nerv. petros. superfic. major. (After Politzer.)
6. Examination of the Ear. The dura is removed from over the temporal bone and the tegmen tympani cut off with chisel and hammer as indicated in Fig. 32, 1, 2, 3, 4, 5, thus exposing the tympanic cavity as shown in Fig. 33. When the tegmen tympani is very hard and compact the hammer and chisel are used to remove that portion of the tegmen lying laterally to the eminence formed by the upper semicircular canals. As the ear-ossicles lie immediately beneath the roof of the tympanic cavity care should be taken not to injure them with the chisel, and this can be best accomplished by beginning to chisel so far posteriorly that the tegmen of the mastoid antrum is first cut away, and from this opening the cut is extended carefully until the tegmen tympani is removed. When the tegmen of the tympanic cavity is very thin and porcelain-like, as is often the case, it may be most quickly and expediently removed by means of the pointed bone-forceps. A complete view of the tympanic cavity is obtained by removing the coverings of the mastoid antrum posteriorly and the bony canal anteriorly after first drawing out the musc. tensor tymp. from the canal. The mastoid process may be opened with the saw or with chisel and hammer. The labyrinth may be exposed by cutting anteriorly with the chisel held horizontally in such a way as to spring off the upper half of the bony labyrinth, exposing the vestibule and cochlea. The superior and posterior semicircular canals come off, and from their open spaces the membranous semicircular canals can be lifted out with the forceps and then examined in water.
The external auditory canal may be opened and the outer surface of the ear-drum examined by carrying the anterior flap of the scalp downward and forward until the entrance into the bony canal is reached. The external ear is then cut off close to the bone, using slight pressure so as to avoid tearing out the lining of the canal or injuring the tympanum. The anterior bony wall of the canal, and a part of the lower, are then carefully chiseled away until the membrane is exposed. Any bony projections on the thicker upper or lower wall of the canal may be trimmed off to give an unobstructed view. When pathologic changes are present upon any part of the wall of the canal the latter should be opened from the other side so as to expose the condition fully.
For the removal of the auditory apparatus and its examination outside of the body a number of methods are advised. The temporal bone may be resected by extending the scalp-incision half-way down the neck along the anterior edge of the trapezius. The anterior flap with the external ear is carried forward as far as the middle of the zygoma and below to the angle of the lower jaw. The posterior flap is carried backward to the middle of the occipital bone. All soft parts are cut as closely to the bone as possible. A saw-cut is now made across the posterior cranial fossa, beginning just behind the mastoid process and extending to the median line of the clivus half-way between the anterior border of the foramen magnum and the sella turcica. The sinus sigmoideus is thus included in the part to be removed. A second saw-cut is then made across the middle cranial fossa, in a line nearly parallel with the transverse diameter of the skull, cutting the middle of the zygomatic arch, the anterior portion of the squama, the great wing of the sphenoid and the pterygoid process, to the tuberculum sellæ. The median ends of the two saw-cuts are then united by a chisel-cut in the median line of the sella and clivus. All bony connections remaining are then cut with the chisel. The soft parts are then cut, beginning with those attached to the mastoid process; the loosened bone is then raised and pulled anteriorly so that the posterior capsule of the maxillary joint can be cut and the jaw-bone disarticulated. All remaining soft parts of neck and nasopharynx are now cut and the temporal bone with the complete ear-apparatus and neighboring portion of nasopharynx is removed. When both temporal bones are removed the saw-cuts should not be carried to the median line, but should stop at the borders of clivus and sella, and then united on each side by sagittal chisel-cuts made along these borders, leaving the clivus and sella as a firm connecting bridge between anterior and posterior portions of the skull. The resected bone may now be examined by means of a saw-cut made perpendicularly through the apex of the eminence of the superior semicircular canals and parallel with the crista of the petrous bone. The tegmen should be removed before the saw-cut is made and the covering of the tympanic cavity and the outer wall of the external auditory canal also removed. The tendon of the tensor tympani is cut and the anvil-stapes articulation severed so that the saw-blade passes between the drum, hammer and anvil on one side and the head of the stapes on the other without damaging or displacing the ossicles. This can be accomplished by pushing outward the drum with hammer and anvil so that the saw-blade can pass between the anvil and the head of the stapes. The bone should be held in a vise and a fret-saw used. On one side of the cut will be seen the drum, hammer, anvil and anterior portion of the mastoid cells; on the other the stapes, wall of the labyrinth and posterior half of the mastoid cells. The Eustachian tube may be easily worked out from the tympanic cavity or from the pharyngeal opening.
A sagittal section of the middle ear may be made, giving pictures as shown in Figs. 34, 35. The temporal bone is resected as above, the tegmen tympani removed and the bony covering of the Eustachian tube removed with hammer and chisel until the tube is exposed from its pharyngeal opening to the isthmus. The temporal bone is then divided into an outer and an inner half by cutting the roof of the tube with fine straight scissors from the pharyngeal mouth to the bony portion and then cutting the membranous floor of the canal likewise. The bony canal, the floor of the tympanic cavity and the mastoid process are then cut sagittally with a fine fret-saw, passing between the lower annular segment of the sulcus tympani and the inner wall of the tympanic cavity. By altering the direction of the saw-cut the Eustachian tube may be removed in connection with either outer or inner portion of the temporal bone.